Scientific results of explorations by the U. S. Fish Commission steamer Albatross. No. VII..Preliminary report on the collection of Mollusca and Brachiopoda obtained in 1887-'88

SCIENTIFIC RESULTS OF EXPLORATIONS BY THE U. S. FISH COMMISSION STEAMER ALBATROSS. [Published by permission of lion. Marshall McDonald, Commissioner of Fisheries.] No. VII.— PRELIMINARY REPORT ON THE COLLECTION OF MOLLUSCA AND BRACHIOPODA OBTAINED IN 1887-'S8. BY William Healev Dall, A. M.. Curator of the Department of Mollusks. (With Plates V to XIV.) Before proceeding to discuss the particular specimens obtained on the voyage of the U. S. Fish Commission steamer Albatross from Fortress Monroe in Chesapeake Bay to Magellan Straits and northward to Cal-ifornia, it may not be improper to say a few words on the conditions under which the deep-sea Mollusks exist, and the reasons why a study of these animals is important for science. In order that their existence may be maintained, the abyssal mollusks require oxygen to aerate their circulation, food to eat, and a foot-hold upon which they may establish themselves. It is necessary that the conditions should be such as will not prevent the development of the eggs by which successive generations are propagated. That they do permit it may be assumed from the very fact that mollusks in large uumbers have been shown beyond all question to exist on the oceanic floor wherever it has been explored. Formerly, when dredging with the usual appliances in small boats, 100 fathoms (GOO feet) was considered extremely deep. If one stauds at the foot of the great Washington obelisk and looks up, the idea of collecting a satisfactory representation of the insects and plants on the ground at its base by dragging a 0-foot trawl or dredge by a line let down from the apex of the monument strikes one as preposterous. Yet the monumeut is less than 100 fathoms high. Multiply this height ten or fifteen times aud the idea seems, if possible, still more unreasonable; yet it is a fact that successful dredging has been done from a height above the sea bottom of not less than twenty-five times the height of the Washington Monument. Living animals have been secured from a depth equalling the distance from the Capitol to Rock Creek, or from the Washington Monument to the Mansion at Arlington — that is to say, about 2i miles. 219 Proceedings of the National Museum Vol. XII— No. 773.